The present invention relates to a series of new penem compounds exhibiting valuable antibiotic activity, to a process for preparing these compounds and to antibiotic compositions containing the compounds as the active agent.
The penicillins form a well known class of antibiotics, which have found considerable use in human and animal therapy for years. Chemically, the penicillins have in common a beta-lactam structure, commonly referred to as "penam", which may be represented by the following formula ##STR2## The structure of many valuable penicillin derivatives has a double bond between the 2- and 3-positions and the resulting structure is known as "penem" and forms the basis for the semi-systematic nomenclature of the penicillins. This semi-systematic system of nomenclature is employed herein.
The basic "penem" structure contains atoms or groups of atoms attached to the carbon atoms at the 2- and 6-positions and will normally contain a carboxy group or derivative thereof (e.g. salt or ester) attached to the carbon atom at the 3-position. Differences in the activities, potencies and other properties of the various penicillin derivatives are dictated by the various groups attached to these positions, but the way in which such groups affect the penicillin derivatives has not been elucidated.
U.S. Pat. No. 4,260,618 discloses a series of penem derivatives having a heterocyclic-substituted thio group at the 2-position.
We have now discovered a series of novel penem derivatives having, at the 2-position, a heterocyclic-substituted thio group in which the heterocyclic ring has two nitrogen atoms, i.e. differing substantially in structure from those disclosed in U.S. Pat. No. 4,260,618. These penem derivatives have been found to have comparable antibacterial activities with and better biological and chemical stability tnan, for example, thienamycin which is one of the most potent and valuable beta-lactam antibiotics currently available.